The present invention relates to secured data transmission in multiuser computer architectures. More particularly, the present invention relates to prevention of unauthorized access to data communicated on local area networks.
A local area network (LAN) is a communications link between data processing equipment located in a limited geographic area. LANs connect personal computers, mini- and mainframe computers, printers and other similar devices implementing a concept that permits programs, data files, and resources to be shared throughout the network.
FIG. 1 contains a diagram of a typical LAN setup. In FIG. 1, the data processing equipment located in a discrete physical area, for example, different buildings, or in a discrete organization, for example, a department, are interconnected to form a local or departmental LAN. In the topology of FIG. 1 these smaller local LANs are interconnected via a backbone 8 by repeaters 10 to form the system-wide LAN.
Repeaters (also known as concentrators or hubs) are devices which regenerate LAN signals received at the repeater input and then output the regenerated signals to individual stations or nodes. Repeaters thus extend maximum network radius. Frames of data applied to any of the repeaters 10 are regenerated by the repeater for faithful rebroadcast to the station(s) or node(s) to which the individual repeater is connected. As illustrated by the repeater 10-3 of FIG. 1, repeaters 10 may also be connected to other repeaters.
The local departmental networks depicted in FIG. 1 may also contain routers and/or bridges 14. The bridges and routers serve to isolate the strictly local departmental traffic from the backbone traffic. Backbone traffic not destined for a local station is not forwarded across the bridge to the departmental LAN. Similarly, strictly local traffic is not forwarded across the bridge and placed on the backbone.
The bridge, however, does nothing to protect the interdepartmental and local traffic on the departmental LAN from being observable by all stations within that departmental LAN. This fact is especially applicable in broadcast based communications protocols, such as Ethernet, wherein all communications within the given LAN are received by all stations in that LAN. Sensitive and valuable user data is thus available to "promiscuous mode" or eavesdropping reception by any station connected to the departmental LAN. The eavesdropping connection can be made on any convenient place on the LAN (e.g., an office outlet) and is virtually undetectable.
The security threat presented by potential eavesdroppers has become increasingly credible as LAN equipment, personal computers, and portable network diagnostic equipment prices continue to drop, thereby making the equipment to eavesdrop readily available. Eavesdropping is also simpler to implement and more difficult to detect than in the past because LAN networks can now be interconnected with the same wiring systems used for telephones rather than the specialty cables required under other, earlier standards.
Merely suspending transmission of data to nodes that are not authorized to receive the data is an unsatisfactory solution in LANs using broadcast-based communication protocol. To do so may result in unacceptable collisions when stations on the "quiet" nodes, seeing no communications traffic, begin transmitting data despite the presence of communications traffic on other nodes of the LAN.
Some limited methods for access control security to counter the eavesdropping threat do exist. However, these existing methods are themselves subject to interception on the LAN. For example, a password, even in its encoded form, must travel through the network and is subject to interception.